1. Field of the Invention
The present invention pertains to a camera using film employing a new system as well as to an external flash device.
2. Description of the Related Art
FIG. 1 shows the size of a frame of film. This frame size is set at 36 mm.times.24 mm based on the dimensions of a roll of J135 film provided in JIS K7519. Conventionally, cameras that perform photo-taking by means of an exposure window with a size matching the frame size of this type of film (hereinafter `135 film`) have been widely used (hereinafter `a 135 type camera or 135 type cameras`).
Some of said conventional cameras use an external flash device that may be mounted onto the camera body. Using such a camera, when an external flash device is mounted onto the camera body, the focal length data regarding the photo-taking lens of the camera is transmitted to the external flash device from the camera body. The external flash device has an auto-zoom function to control the angle of irradiation and amount of light based on the focal length data thus received, and also displays said focal length via a display unit.
FIG. 2 is a drawing to explain the relationship between focal length f of the photo-taking lens of camera 1 and angle of irradiation .phi. of external flash device 2. In the drawing, the distance between film surface S1 and object plane S2 is deemed d. In addition, the angle of view when focal length f=f1 is deemed .theta.1, and the angle of irradiation required in that instance is deemed .phi.1. The angle of view when focal length f=f2 is deemed .theta.2, and the angle of irradiation required in that instance is deemed .phi.2.
As shown in FIG. 2, when the relationship f1&lt;f2 exists, the corresponding relationship .theta.1&gt;.theta.2 results. Therefore, in order to irradiate the entire object plane S2 with the light emitted by the flash device, the angle of irradiation required of external flash device 2 is .phi.1 &gt;.phi.2. In other words, as focal length f increases, the angle of irradiation required decreases.
Film employing a new system with a frame size of 30.2.times.16.7 mm, as shown in FIG. 3, (hereinafter `new type film`) has recently been proposed, and an attempt has been made to popularize the use of cameras that perform photo-taking via an exposure window of a size matching the new type film frame size (hereinafter `a new type camera or new type cameras`) together with the new type film.
Because new type film and 135 film have different frame sizes, when the object on object plane S2 is exposed onto the film located at film surface S1 using photo-taking lenses having an equal focal length, as shown in FIG. 4, if the angle of view for 135 film is .theta.11 and that for new type film is .theta.12, the relationship between the angles of view is .theta.11&gt;.theta.12. Therefore, if the maximum size of the object on object plane S2 that may be photographed is L11 for 135 film and L12 for new type film, L11&gt;L12 results.
Incidentally, where photo-taking is performed using the same angle of view, it is necessary to make the focal length of the photo-taking lens of a new type camera shorter than that of the photo-taking lens of a 135 type camera, and because this relationship is proportional to the ratio of the frame sizes of the two types of film, the focal length of the photo-taking lens of a new type camera must be approximately 0.8 times that of the photo-taking lens of a 135 type camera.
Therefore, considering the relationship between focal length f and angle of irradiation .phi. explained with reference to FIG. 2, the angle of irradiation required of the external flash device for a 135 type camera (hereinafter `135 type flash device`) differs from that required of the external flash device for a new type camera (hereinafter `new type flash device`).
FIGS. 5a and 5b are drawings that show in a simplified fashion the photo-taking ranges for each type of film, or in other words, the angles of view (solid lines) and the angles of irradiation of corresponding external flash devices (chain lines). FIG. 5a shows the situation in which 135 film is used, while FIG. 5b shows the situation in which new type film is used.
As shown in FIG. 5a, the 135 type flash device has a wide angle of irradiation corresponding to 135 film that has a large angle of view. On the other hand, as shown in FIG. 5b, the new type flash device has an angle of irradiation smaller than that of the 135 flash device, corresponding to new type film that has an angle of view smaller than that of 135 film.
Therefore, if a 135 type camera, 135 type flash device, new type camera and new type flash device are used in random combination, the problems described below occur in connection with the display of the focal length in the display unit of the external flash device and in connection with the angle of irradiation during light emission.
Table 1 indicates whether the angle of irradiation of the flash device and the focal length display are acceptable in each combination of a new type camera or 135 type camera, both said cameras having a 28 mm focal length photo-taking lens, and a new type flash device or 135 type flash device, as one example. In Table 1, the 135 type camera and new type camera transmit the focal length data regarding the photo-taking lens to the external flash device without any processing.
TABLE 1 __________________________________________________________________________ Combination Angle of irradiation Focal length display Flash Accetab- Accetab- device Camera Illustration ility Display value ility __________________________________________________________________________ 1 New type New type 1 #STR1## .largecircle. 28 mm .largecircle. 2 135 type New type 2 #STR2## .largecircle. 28 mm .largecircle. 3 New type 135 type 3 #STR3## X 28 mm .largecircle. 4 135 type 135 type 4 #STR4## .largecircle. 28 mm .largecircle. __________________________________________________________________________
Regarding the focal length display in the display unit of the external flash device, since the focal length data regarding the photo-taking lens is transmitted without any processing to the external flash device from the camera in each combination, an accurate display is obtained in all combinations (1) through (4), as shown in Table 1.
Regarding the angle of irradiation, in combination (2) in which a 135 type flash device is mounted to a new type camera, the angle of irradiation covers the angle of view for 135 film, which is larger than that for new type film. In combination (1) in which a new type flash device is mounted to a new type camera and combination (4) in which a 135 type flash device is mounted to a 135 type camera, the angle of irradiation and the frame size match each other.
On the other hand, because a new type flash device emits light across an angle of irradiation for the angle of view for new type film when the focal length is 28 mm, in combination (3) in which a new type flash device is mounted to a 135 type camera, the angle of irradiation cannot cover the entire angle of view for 135 film which is larger than that of new type film.